Formal:
* Stated
* Declared
* Announced
* Asserted
* Remarked
* Observed
* Expressed
Informal:
* Spoke
* Told
* Mentioned
* Added
* Noted
* Whispered
* Shouted
Figurative:
* Utter
* Proclaim
* Pronounced
* Articulated
* Verbalized
Specific to the speaker:
* He/She/They/It murmured
* He/She/They/It whispered
* He/She/They/It confided
* He/She/They/It grumbled
* He/She/They/It chuckled
To choose the best synonym, consider the tone, the speaker and the context of the sentence.